<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        /**
         * 变量
         */ 
        var a = 5 
        var b = 8;
        c = 9
        var d;
        d = 4


        {
            var m = 1 // 全局的
            let n = 2 // 块级作用域
        }
        // alert(n)

        const x = 7
        // x = 8


        /**
         * 输入和输出
         */ 
        // alert('hello world')
        // console.log('hello world')

        var age = prompt('请输入您的年龄：')
        console.log(typeof age) // string
        age = Number(age)
        console.log(typeof age) // number
        console.log(age + 1)

    </script>
</head>
<body>
    
</body>
</html>